A conventional rotary head drum device used for a video tape recorder is configured as shown in FIG. 11.
Reference numeral 1 denotes a fixed drum for guiding a magnetic tape (not shown), reference numeral 2 denotes a shaft which is coaxially fixed on the fixed drum 1, reference numeral 3 denotes a rotary drum having a magnetic head 4 on the lower surface, reference numeral 5 denotes ball bearings located on the upper part and the lower part of the rotary drum 3, reference numeral 6 denotes a rotation-side rotary transformer which is bonded to a lower bonded surface 3a of the rotary drum 3 via an adhesive and is electrically connected to the magnetic head 4. Reference numeral 7 denotes a fixation-side rotary transformer which is opposed to the lower surface of the rotation-side rotary transformer 6, is bonded to an upper bonded surface 1a of the fixed drum 1, and is electrically connected to an amplifying section (not shown).
Such a rotary head drum device is disclosed in Japanese Patent Publication No. 5-6244, for example.
As shown in FIG. 12, the rotation-side rotary transformer 6 is bonded to the rotary drum 3 and the fixation-side rotary transformer 7 is bonded to the fixed drum 1. Reference numeral 8 denotes an adhesive layer for boding the fixed drum. 1 and the fixation-side rotary transformer 7, reference numeral 9 denotes an adhesive layer for bonding the rotary drum 3 and the rotation-side rotary transformer 6.
Further, in order to obtain a signal transmission characteristic between the rotation-side rotary transformer 6 and the fixation-side rotary transformer 7, a gap A formed by the lower surface of the rotation-side rotary transformer 6 and the upper surface of the fixation-side rotary transformer 7 is generally set as an interval of several tens μm, and a surface runout accuracy is defined at A/2 or less for each of the rotation-side rotary transformer 6 with respect to the axis of rotation of the rotary drum 3 and the fixation-side rotary transformer 7 with respect to the axis of rotation of the shaft 2 fixed on the fixed drum 1.
In this rotary head drum device, information including an image and sound is recorded on a magnetic tape (not shown) through a path of the amplifying section (not shown)→the fixation-side rotary transformer 7→the rotation-side rotary transformer 6→the magnetic head 4 by rotating the rotary drum 3 including the magnetic head 4. Further, in the case of a recorded magnetic tape (not shown), recording information is reproduced through a path of the magnetic head 4→the rotation-side rotary transformer 6→the fixation-side rotary transformer 7→the amplifying section (not shown).
Such a rotary head drum device has been conventionally fabricated in the process below.
First, the magnetic head 4 is attached to the rotary drum 3, and the ball bearings 5 are located on the upper part and the lower part of the inner surface of the bearing hole of the rotary drum 3. Next, after an adhesive is applied to the lower bonded surface 3a of the rotary drum 3, the rotation-side rotary transformer 6 is fixed thereon by bonding with pressure.
Next, an adhesive is applied to the upper bonded surface 1a of the fixed drum 1, and the fixation-side rotary transformer 7 is fixed thereon by bonding with pressure.
Then, the shaft 2 fixed to the fixed drum 1 is inserted through the shaft hole of the ball bearings 5 provided for the rotary drum 3, the rotary drum 3 is fixed with respect to the axial direction of the shaft 2, the rotary drum 3 is mounted so as to rotate about the axis of the shaft 2, and thus the rotary head drum device is obtained.
However, the adhesive layer 8 or the adhesive layer 9 have an uneven thickness because an amount or an applied position of the adhesive between the rotary drum 3 and the rotation-side rotary transformer 6 varies and an amount or an applied position of the adhesive between the fixed drum 1 and the fixation-side rotary transformer 7 varies. Hence, it is difficult to set a surface runout accuracy of the rotation-side rotary transformer 6 and a surface runout accuracy of the fixation-side rotary transformer 7 at A/2 or less.
In this case, an amount of the adhesive is set at a specified amount with a certain permissible range.
Moreover, the ball bearings 5 are located on the inner peripheral side of the lower bonded surface 3a of the rotary drum 3, and excessive adhesive between the lower bonded surface 3a of the rotary drum 3 and the rotation-side rotary transformer 6 flows into the ball bearings 5 during bonding with pressure, resulting in an adverse effect on the ball bearings 5.